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Annual to subshrub (2)5–70(200) cm; proximal stem and leaves glabrous to variously hairy.
Stem: 1, erect, or 2–25+, prostrate to ascending, simple or branched.
Leaf: simple, alternate, often crowded proximally, petioled, generally ± elliptic to ovate or obovate, generally deeply 1–4-pinnately lobed, occasionally entire (then linear), lobes generally not or scarcely overlapping; distal generally ± reduced.
Inflorescence: heads discoid or radiant, 1–25+ per stem, generally in terminal cyme-like cluster; peduncle generally erect, hairs generally as on phyllary bases; involucre generally <= 15[25] mm diam, cylindric to obconic or hemispheric; phyllaries in 1–2 ± = series, generally linear to lanceolate, persistent, tips generally ± flat, generally ± green; receptacle flat to rounded, glabrous, generally epaleate.
Flower: 8–70+; corolla white, ± pink, or yellow, generally open during day; anthers generally exserted, tips lanceolate to ovate; style tips linear, minutely bristly.
Fruit: ± club-shaped, generally not compressed, ± hairy; pappus 0, crown-like, or generally of (1)4–20 persistent, ± fringed scales in 1–4 series, scales often fewer and/or shorter on outer fruit.
18 species: w North America. (Greek: gaping ray, for enlarged outer corollas of type sp.) [Morefield 2006 FNANM 21:400–414] Spp. of sect. Chaenactis hybridize, especially in SCoRI/s SnJV, where identification can be difficult.

Key to Chaenactis

1. Perennial (biennial) or subshrub, rarely flowering first yr; inner fruit pappus generally of 10–20 scales in 3–4 ± equal series; leaf blade gland-pitted under hairs; heads discoid (sect. Macrocarphus)

2. Lvs generally cauline (also basal in Chaenactis douglasii); heads not scapose, (1)2–25+ per stem; plants not or scarcely cespitose or matted

3. Perennial or biennial, rarely flowering first yr or slightly woody; proximal hairs cobwebby to tomentose, ± gray, thinning with age; basal leaves generally persistent, largest leaf blades ± elliptic, not flat ..... C. douglasii var. douglasii

3' Generally subshrub; proximal hairs (especially stems) ± felty, ± white, persistent; basal leaves generally 0, largest leaf blades ± deltate, ± flat

4. Longest phyllaries 10–13 mm, outer ± tomentose, not or scarcely glandular; e PR ..... C. parishii

4' Longest phyllaries 14–18 mm, outer generally glandular-hairy, other hairs 0 or scarce; e KR, n CaRH ..... C. suffrutescens (2)

2' Lvs ± basal; heads ± scapose, 1(3) per stem; plants cespitose to ± matted

5. Outer phyllaries silky-tomentose, nonglandular ..... C. alpigena

5' Outer phyllaries generally glandular-hairy, often also cobwebby to woolly or shaggy-hairy

6. Largest leaf blades ± deltate to ovate, ± flat; 1° lobes generally 2–4(5) pairs, tips ± flat

7. Plant 2–10(12) cm; leaves 2.5–5 cm; longest phyllaries 9–12(14) mm; corolla 5.5–8 mm; longest pappus scales 3–5 mm ..... C. nevadensis

7' Plant (10)25–45(60) cm; leaves 5–10 cm; longest phyllaries 14–18 mm; corolla 8.5–10 mm; longest pappus scales 7–9 mm ..... C. suffrutescens (2)

6' Largest leaf blades ± elliptic or cylindric to ± fusiform, not flat; 1° lobes (4)5–18+ pairs, tips curled and/or twisted

8. Largest leaf blades ± elliptic; 1° lobes (4)5–9(12) pairs, not or scarcely overlapping ..... C. douglasii var. alpina

8' Largest leaf blades cylindric to ± fusiform; 1° lobes (7)10–18+ pairs, ± overlapping ..... C. santolinoides

1' Annual; inner fruit pappus 0, crown-like, or of 4(5) or (7)8 scales in 1 or 2 unequal series, outer << inner; leaf blades (except Chaenactis macrantha) not gland-pitted; heads discoid or radiant

9. Proximal hairs mealy, scaly, or powdery; largest leaf blades generally ± deltate, (2)3–4-pinnately lobed (sect. Acarphaea)

10. Phyllary tips acute or scarcely acuminate, ± flat, ± green; leaf lobe tips ± flat; receptacle epaleate; fruit compressed; pappus 0 or longest scales <= 0.5 mm ..... C. artemisiifolia

10' All or inner phyllary tips long-acuminate, needle-like, ± red; leaf lobe tips ± cylindric; receptacle paleate; fruit not compressed; longest inner fruit pappus scales generally 3–5 mm ..... C. carphoclinia

11. Lvs basal and cauline, longest 1–6(7) cm; petiole slender, flexible, base scarcely enlarged ..... var. carphoclinia

11' Lvs generally basal, longest 7–10 cm; petiole thick, stiff, base strongly enlarged ..... var. peirsonii

9' Proximal hairs cobwebby to woolly or 0; largest leaf blades linear, entire, or ± elliptic (to ovate), 1–2-pinnately lobed (sect. Chaenactis)

12. Corolla white to ± pink or rarely pale yellow; generally in or near GB, D

13. Heads radiant; peduncle distally generally glandular-hairy, or ± glabrous in fruit; outer corollas bilateral, spreading, > inner; inner fruit pappus generally of 4 scales in 1 series

14. Longest pappus 6–8.5 mm, exceeding corolla, tips visible among buds; proximal hairs 0 by flower time; largest leaf blades entire or 1-pinnately lobed, lobes generally 1–2(5) pairs; outer phyllaries ± glabrous in fruit, tip acute ..... C. fremontii

14' Longest pappus 1.5–6 mm, not exceeding corolla, tips hidden; proximal hairs persisting at least at nodes by flower time; largest leaf blades generally 1–2-pinnately lobed, 1° lobes 4–8 pairs; outer phyllaries glandular-hairy and/or ± cobwebby in fruit, tip ± obtuse ..... C. stevioides

13' Heads discoid; peduncle nonglandular; outer corollas radial, spreading or not, ± = inner; pappus of (6)8 scales in 2 unequal series, outer << inner

15. Corolla open at night, anthers ± included; inner corollas 9–12(15) mm, 1.8–2.2 × fruit; leaf blades ± gland-pitted under hairs ..... C. macrantha

15' Corolla open during day, anthers exserted; inner corolla 4–10 mm, ± = fruit; leaf blades not gland-pitted

16. Longest phyllaries 10–18 mm, outer nonglandular, glabrous proximally, densely puberulent distally, tip generally recurved, flexible; pappus scales 8 ..... C. xantiana

16' Longest phyllaries 4.5–10(12) mm, outer generally glandular-hairy, hairs otherwise various, uniform, tip erect, stiff; pappus scales generally < 8 (hybrids; see genus note)

12' Corolla bright to dark yellow; generally CA-FP ..... C. glabriuscula

17. Inner fruit pappus generally of 7–8 scales in 2 series, outer << inner ..... var. heterocarpha

17' Inner fruit pappus generally of 4 scales in 1 series

18. Proximal hairs tomentose to woolly, ± white; leaves ± basal, persistent ..... var. lanosa

18' Proximal hairs 0 or ± cobwebby, ± gray; leaves basal (withering) and cauline

19. Largest leaf blades generally 2-pinnately lobed, fleshy; stem ± spreading; SCo, coastal dunes, bluffs ..... var. orcuttiana

19' Largest leaf blades 1(2)-pinnately lobed, scarcely fleshy; stem erect to ascending; inland from coast

20. Longest phyllaries 5–7 mm, 1–2 mm wide, outer ± silky-cobwebby at least medially in fruit, often also ± glandular-hairy; longest pappus 2–4 mm, 0.4–0.7 × corolla ..... var. glabriuscula

20' Longest phyllaries 7–9 mm, 2–3 mm wide, outer becoming glabrous in fruit; longest pappus generally 5–8 mm, ± 0.9(1) × corolla ..... var. megacephala

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